Known in the art is a drill disclosed in USSR Inventor's Certificate No. 718232 issued July 28, 1978 and published 1980, comprising a holder and a cutting member in the form of a pair of discs mounted in the holder eccentrically with respect to the axis thereof, the discs partly engaging each other with their end faces which have recesses to receive an insert for setting a desired diameter of drilling. This drill may be successfully used for counterboring. Since the cutting member of the drill comprises two round discs secured to each other, it cannot be used for drilling in a continuous body of material as the cutting edge of one disc at the center of the head portion of the drill is situated in the immediate proximity to the clearance face of the other disc. In drilling a hole in a continuous body of material, the root of chip (in the area where the chip has a high enough rigidity) bears against the clearance face of the cutting disc and the chip would get in between the engaging end faces of the cutting discs. The chip getting in between the discs hampers the cutting process, and causes a temperature increase in the cutting zone so that the drill life is reduced. In addition, the diametrical size of the drill is at rather a large distance from the head end face of the holder and is equal to about 2/3 R wherein R is the radius of the cutting disc. Therefore the diagonal of holder cross-section cannot exceed the diameter of the hole being machined in a plane drawn at a distance of 2/3 R from the center line of the cutting discs, i.e. the distance from the head end face of the holder to the center line of the cutting discs should be kept minimum possible so that the holder might have maximum possible cross-sectional area. A small cross-sectional area of the holder cannot ensure necessary rigidity of the drill.
It should also be noted that in machining holes in a continuous body of material only about one fourth of the whole circular cutting edge of each disc can take part directly in the cutting process (with one setting of the cutting member) so that the drill life is reduced as compared to penta- and hexahedral discs.